Process for the production of cyclohexanone oxime



PRocEss FOR rrmrnonuciriorl 'UFCYCLO- "HEXANQNE 'OXIME Lorraine GuyDOEIBTHHIQ, Woodbury, N. =J.,'assignor to E.;-I. du Pont'de Nemours -andCompany, Wilmington,

Del., a corporation of Delaware No Drawing. Application May 1a, 1955,Serial No. 507,485

5 Claims. (Cl. 260-566) The 'presentinvention relates to 'an'improv edprocess for the production of a' capr'olactamintermediate and,

'more particularly, to an improved process forthe "production ofcyclohexanone oxime.

KetoXirnes, particularly -cycloalkanone*oximes, have long been 'used asintermediates 'in the preparation of amides and lactams. For example,cyclohexanoue' oxime, the most'important member or" this class,hasserved as an intermediate for the preparation of caprol-actam whichis produced by Beclrmann rearrangement of theoxime. It

"has also previously been known to produce the cyclohexanone oxirne andother cycloaikanone and alkano'ne 'oximes by treatment of *theappropriate nitrocycloalkane ornitro alkane salts with stannouschlor'ideand strong mineral acid. The use of theless expensiveferrous chlo-'ride'as the reducing agent has also been mentioned inthe -literature,but low conversions to the desired oximesand high conversions'totheundesiredketones were experienced with theme of theferrous'salt.Nevertheless, he-

cause ferrous chloride is acheap,readily available reagent, t'heneed haslong been felt fora process wherein ferrous salts could be used toproduce cycloalkauone oximesin high yield from nitro cycloalkane-saltswithout'the attend anfiformation of large amounts of theundesir'ed-ketones.

Accordingly, an object of the present invention is to "provideanimproved, economical process for the productionof a caprolactamintermediate. Another object ofthe presentiuvention is to provide anefficient process =for the production of cyclohexanone oxime'wherein theformation of large quantities of undesirable by-product is avoided. Astill further object of the present invention is toprovidea simple,economical process for'the conversion of water-soluble saltsofnitrocyclohexane to'a useful product. Other objects will becomeapparent as the invention is further described.

I have found that the foregoing objects may be achieved and'thedisadvantages of the prior processes overcome when I introduceseparately into a reaction zone containing a-concentrated solution of amineral acid, an aqueous solution of an alkali metal salt ofnitrocyclohexane, and at-ferrous salt at rates such that-the molar ratioor the ferrous salt to the salt of nitrocyclohexane ismaintained at-alltimes between 1.7 to l and 2.5 to 1.

Iii-accordance with the process'of the present invention,

"into a reaction Zone containing asolutiorr of a concentrated mineralacid, e. g., sulfuric acid or hydrochloric aoid,--are introducedseparately an aqueous solution of an alkali metal salt ofnitrocyclohexane, 'e.g.,' the potassium ates PatentC of the presentinvention. However, they will be understood to be illustrative only andnot to limit the invention 9,2 in any manner. The partstgiveri-in theexamples are parts by weight.

Example 1 To parts of3'7%hydrochloric acidiwerevaddedrcontinuously.soli'cl ferrous chloride .tetrahydratevandt a 259 M solution of thepotassium salt 10f initr'ocyclohexane, ithe rates of addition being suchthat-the'molarrratio'zoftthe ferrous salt to the initrocyclohexane "salt"was maintained .at-Z to l andvthe-temperature washeld betweeniahoutiOand about3O C. After-40 ,parts of the ferrous chloride tetrahydrate and17 :partsof the'zpotas'sium nitrocyc-lohexane had been added, the pH-ofthe'reaction mixture was regulated to 5-6 by the addition of ammonia.The reaction. mixture then was extractedcontinuously'forisevoral-hoursWith ether. The extract was dried, concentrated, and the concentrate wasextracted "with-20% sulfuric acid. The pH of-the acidtextract wasadjusted to 5-6, and the product was removed by rfiltration. Thefiltrate was extractedwith ether to obtain'additionalproduct.Cyclohexanone voxime was obtained=in .the amount -of 8.4. parts, a yieldof 74%.

lated'that the mole ratio of'theferrous salt to the potassium'salt wasl.7ito l. .After"39-.6 ,par'ts of the-ferrous salt and 16.6 parts of thenitrocyclohexane salt had been added, the pilot the reaction mixture wasadjusted to 56. When the work-up method employed-in the run of "Example1 was used,there wasobtaine'dfilO parts(53% yield) of cyclohexanoneoxirne.

Example 3 i-ldlidferrous chloride tetrahydrateand a 2.9 'M' solution'of' potassiumnitrocyclohexane were added continu- "ously'to'75 parts of37% hydrochloric acidat aboutZO to 30 C. at a rate such thatthemolafrzitio ofthe ferrous salt tothe nitrocyclohexanesaltwas'maintainedto 2.5 "to l. 'AfterSO parts ofthe ferrous salt 'and17'parts'of the potassium nitrocyclohexane had been added, the 1 pH of thereaction mixture was adjusted 'to "5-6, and the mixture'was'workedup-asin Example 1. 'Cyclohexanone oxime wasobtained in the amount'of-'6.2pa'rts (-55% yield) Example 4 A 2.2 M solution ofthepotassiumsaltof nitrocyclo hexane and-solid ferrous chloride*tetrahydrate"wereradded continuously and simultaneouslyt-o 75 parts of37%;hy drochloric acid at .-2030 C. .The additionswererregu- 'lated tokeep the molar ratio of the. ferrous. salt to the potassium salt at 2.3to 1. --After 40 partsofthe ferrous salt and 17 parts of the. potassiumnitrocyclohexane -had been added, the pH of the reaction-mixture wasadjusted tolabout 6. The reaction mixture was treated according to themethod of Example" 1. CycloheX-anone oxime was obtained in the amountiof9. 1;parts,' a yield of"%.

Example 5 To ll3 parts of 24Nsulfuric acid'wereaddedcon- "tinuouslysolid ferrous chloride tetrahydrate and a 2.9' M

solution of f .the potassium 1 salt of 'anitr-ocycl'ohexane at -aratesuchthatthenmolar. ratio of the ferrous salt to the mtrocyclohexanesalt was maintainedatat 2::rto 1 and-Jithe .-temperature of the-reactionmixture was :1held4b'etWeen aboute25 and about 40 LC. whenz40parts:of-ithe' ferrous salt and 17 parts of the potassium nitrocyclohexanehad been added, the pH of the reaction mixture was adjusted Example 6 Amixture of 13 parts (0.1 mole) of nitrocyclohexane and 6 parts (0.1mole) of potassium hydroxide in 30 parts of water was added slowly atabout 2530 C. to a wellagitated mixture of 40 parts (0.2 mole) offerrous chloride tetrahydrate in 75 parts of 37% hydrochloric acid. Whenthe addition was complete, the pH of the reaction mixture was adjustedto about 4 by the addition of ammonia, and the mixture then wasextracted continuously with ether for several hours. The extract wasdried and the ether was removed by distillation under reduced pressure.The residue consisted of 4.5 parts (40% yield) of cyclohexanone oxime.

Cyclohexanone oxime was obtained in good yields (50% or greater) in theprocess of the invention when, as the runs of Examples 1 to 5illustrate, the ferrous salt and the alkali metal salt ofnitrocyclohexane were intro duced into the reaction zone containing aconcentrated solution of a mineral acid at rates such that the molarratio of the ferrous salt to the salt of nitrocyclohexane was maintainedthroughout the introduction between 1.7 to 1 and 2.5 to l. Themaintenance of the ferrous salt to nitrocyclohexane salt molar ratio inthis range throughout the introduction into the acid is critical in thepresent process. For example, Example 6 illustrates the relatively poorconversion to the oxime obtained in a run in which the final molar ratioof the ferrous salt to the nitrocyclohexane salt was 2 to l but in whichthe actual molar ratio of the ferrous salt to the nitrocyclohexane salt,as controlled by the rate of introduction of the nitrocyclohexane saltinto the acid ferrous salt solution, was much greater than the rangebetween 1.7 to 1 and 2.5 to 1 for the greater portion of theintroduction period. While I do not wish to be limited by a discussionof the reactions which may occur in the present process, the presence atany time during the introduction of the reactants into the acid of alarge excess of the ferrous salt over that theoretically required toeffect reduction (2 moles per mole of the nitrocyclohexane salt)apparently causes hy drolysis of a considerable portion of the oximeformed. This hydrolysis would explain the relatively poor overallconversions to the oxime and the large amounts of ketone obtained bothin the run of Example 6 and in prior processes in which the reducingagents were present in greater than stoichiometrically equivalentquantities during at least a portion of the reduction period.

The process of the present invention may be carried out at temperaturesbetween about 20 and about 70 C. However, as the examples show, the useof a temperature range in which no external heating or cooling isrequired (2030 C.) gave entirely satisfactory yields of the desiredoxime, and this range is preferable from an economic standpoint.Temperatures above about 70 C. cause excessive decomposition of theproduct. The temperature range below 20 C. can be used in the presentprocess but is generally not considered desirable because externalcooling and increased reaction times are required.

The preceding examples additionally illustrate a method of recoveringthe cyclohexanone oxime prepared by the present process. For example,following the addition of the ferrous salt and the nitrocyclohexane saltto the reaction zone containing the concentrated solution of mineralacid, the pH of the reaction mixture can be adjusted by the addition ofany suitable basic material to between about 2 and about 9 and the oximerecovered therefrom, e. g., by one or more extractions.

. The process of the present invention is not limited to the materialsemployed in the foregoing examples. For

example, sodium nitrocyclohexane can be employed. Likewise, the ferrouschloride can be replaced by other ferrous salts. The present process isnot only applicable to the production of cyclohexanone oxime. Forexample, oximcs of cyclopentanone, substituted cyclohexanones andcyclopentanones, cycloheptanone, acetone, and like ketoximes can beprepared, and, correspondingly, salts of nitrocyclopentane, substitutednitrocyclohexanes and nitrocyclopentanes, nitrocycloheptane,2-nitropropane, and like nitro compounds can be used as startingmaterials.

The cyclohexanone oxime prepared by the process of the present inventionis a valuable caprolactam intermediate. For example, the oxime can berearranged to e-caprolactam by a suitable rearrangement process, e. g.,by the process taught in U. S. Patent 2,487,246, issued November 8,1949. However, the use of the oxime product of the process of thepresent invention is not limited to the production of caprolactam. Thecyclohexanone oxime prepared by the present process is also useful as asolvent, as an intermediate for chemical syntheses, and the like.

The invention has been described in detail in the foregoing. It will beapparent to those skilled in the art that many variations can beintroduced without departing from the scope of the invention. I intend,therefore, to be limited only by the following claims.

I claim:

1. A process which comprises introducing separately into a reaction zonecontaining a concentrated aqueous solution of a mineral acid of thegroup consisting of sulfuric acid and hydrochloric acid an aqueoussolution of an alkali metal salt of nitrocyclohexane and ferrouschloride, the rate of introduction of each being so regulated that themolar ratio of the ferrous salt to the salt of nitrocyclohexane presentin said reaction zone is maintained at all times between 1.7 to 1 and2.5 to 1.

2. The process as claimed in claim 1, wherein the alkali metal salt ofnitrocyclohexane is the potassium salt of nitrocyclohexane.

3. A process for the production of cyclohexanone oxime which comprisesintroducing separately into a reaction zone containing a concentratedaqueous solution of a mineral acid of the group consisting of sulfuricacid and hydrochloric acid an aqueous solution of an alkali metal saltof nitrocyclohexane and ferrous chloride, the rate of introduction ofeach being so regulated that the molar ratio of the ferrous salt to thesalt of nitrocyclohexane present in said reaction zone is maintained atall times between 1.7 to 1 and 2.5 to 1, and the temperature beingmaintained between about 20 and about C.

4. A process for the production of cyclohexanone 0xime which comprisesintroducing separately into a reaction zone containing a concentratedaqueous solution of a mineral acid of the group consisting of sulfuricacid and hydrochloric acid an aqueous solution of an alkali metal saltof nitrocyclohexane and ferrous chloride, the rate of introduction ofeach being so regulated that the molar ratio of the ferrous salt to saltof nitrocyclohexane in said reaction zone is maintained at all timesbetween 1.7 to 1 and 2.5 to l and the temperature being maintainedbetween about 20 and about 70 C., adjusting the pH of the reactionmixture to between about 2 and about 9 and thereafter recoveringcyclohexanone oxime.

5. The process as claimed in claim 4, wherein the ferrous salt isintroduced in the form of an aqueous solution.

'Grundmann: Angewandte Chem, vol. 62 (1950), page 558.

1. A PROCESS WHICH COMPRISES INTRODUCING SEPARATELY INTO A REACTION ZONECONTAINING A CONCENTRATED AQUEOUS SOLUTION OF A MINERAL ACID OF THEGROUP CONSISTING OF SULFURIC ACID AND HYDROCHLORIC ACID AN AQUEOUSSOLUTION OF AN ALKALI METAL SALT OF NITROCYCLOHEXANE AND FERROUSCHLORIDE, THE RATE OF INTRODUCTION OF EACH BEING SO REGULATED THAT THEMOLAR RATIO OF THE FERROUS SALT TO THE SALT OF NITROCYCLOHEXANE PRESENTIN SAID REACTION ZONE IS MAINTAINED AT ALL TIMES BETWEEN 1.7 TO 1 AND2.5 TO 1.